Articles | Volume 34, issue 1
Ann. Geophys., 34, 1–15, 2016
Ann. Geophys., 34, 1–15, 2016

Regular paper 15 Jan 2016

Regular paper | 15 Jan 2016

Mass-loading, pile-up, and mirror-mode waves at comet 67P/Churyumov-Gerasimenko

M. Volwerk1, I. Richter2, B. Tsurutani3, C. Götz2, K. Altwegg4, T. Broiles5, J. Burch5, C. Carr6, E. Cupido6, M. Delva1, M. Dósa7, N. J. T. Edberg8, A. Eriksson8, P. Henri7, C. Koenders2, J.-P. Lebreton9, K. E. Mandt5, H. Nilsson10, A. Opitz7, M. Rubin4, K. Schwingenschuh1, G. Stenberg Wieser10, K. Szegö7, C. Vallat11, X. Vallieres9, and K.-H. Glassmeier2 M. Volwerk et al.
  • 1Space Research Institute, Austrian Academy of Sciences, Graz, Austria
  • 2Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, Germany
  • 3California Institute of Technology, Pasadena, California, USA
  • 4Physikalisches Institut, University of Bern, Bern, Switzerland
  • 5Southwest Research Institute, San Antonio, Texas, USA
  • 6Space and Atmospheric Physics Group, Imperial College London, London, UK
  • 7Wigner Research Centre for Physics, Institute for Particle and Nuclear Physics, Hungarian Academy of Sciences, Budapest, Hungary
  • 8Swedish Institute of Space Physics, Uppsala, Sweden
  • 9Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Orleans, France
  • 10Swedish Institute of Space Physics, Kiruna, Sweden
  • 11Rosetta Science Ground Segment, European Space Astronomy Centre, Madrid, Spain

Abstract. The data from all Rosetta plasma consortium instruments and from the ROSINA COPS instrument are used to study the interaction of the solar wind with the outgassing cometary nucleus of 67P/Churyumov-Gerasimenko. During 6 and 7 June 2015, the interaction was first dominated by an increase in the solar wind dynamic pressure, caused by a higher solar wind ion density. This pressure compressed the draped magnetic field around the comet, and the increase in solar wind electrons enhanced the ionization of the outflow gas through collisional ionization. The new ions are picked up by the solar wind magnetic field, and create a ring/ring-beam distribution, which, in a high-β plasma, is unstable for mirror mode wave generation. Two different kinds of mirror modes are observed: one of small size generated by locally ionized water and one of large size generated by ionization and pick-up farther away from the comet.

Short summary
The solar wind magnetic field drapes around the active nucleus of comet 67P/CG, creating a magnetosphere. The solar wind density increases and with that the pressure, which compresses the magnetosphere, increasing the magnetic field strength near Rosetta. The higher solar wind density also creates more ionization through collisions with the gas from the comet. The new ions are picked-up by the magnetic field and generate mirror-mode waves, creating low-field high-density "bottles" near 67P/CG.